Using multiple accounts simultaneously

After the G Suite transition, you'll find that you can't sign into another Google Account in the same browser while you’re signed in to an account you use through your work, school, or other organization. Here's why:

The Google sign-in cookie only lets you sign in with one account at a time.

In the past, G Suite accounts were cookied separately from Google Accounts, so you could sign in to both your Google Account and your G Suite account in the same web browser.

Your G Suite account has undergone a transition, and now functions more like a full Google Account. Your account uses the standard Google sign-in cookie, allowing you to sign in to only one account at a time.